1. Field of the Invention
The present invention relates to a method of obtaining a semiconductor wafer having a high degree of flatness and little processing-induced strain from a monocrystalline ingot, in particular a method of manufacturing a semiconductor wafer in which an improvement in manufacturing efficiency is achieved by grinding with a double-headed grinding machine, and moreover minute surface undulations produced by the grinding are reduced and hence a more uniform surface is obtained.
2. Description of the Related Art
The following steps are generally used in a method of manufacturing a semiconductor wafer: 1) a slicing step of slicing a monocrystalline ingot pulled using a monocrystal pulling device to obtain a thin disk-shaped wafer; 2) a chamfering step of chamfering the sliced wafer to prevent chipping or cracking; 3) a lapping step to flatten the chamfered wafer; 4) an etching step to remove a processing-induced strained layer that appears on the wafer as a result of the aforementioned processing; 5) a polishing step of finish-polishing the chamfered part; 6) a polishing step of polishing either one or both surfaces of the wafer; and 7) a finish-polishing step of finish-polishing the wafer.
For the purpose of reducing the number of manufacturing steps or the amount of polishing and improving the flatness of the wafer produced, a method in which chamfering is carried out after slicing, then planar grinding of both surfaces is carried out, and then finishing is carried out by chemical polishing (Japanese Patent Application Laid-open No. H8-31680) and a method in which planar grinding of both surfaces is carried out after slicing, then etching to remove residual strain is carried out if necessary, and then both surfaces are finished by chemical polishing (Japanese Patent Application Laid-open No. H9-248740), have been proposed.
Moreover, for the purpose of simplifying the manufacturing process and improving the flatness, a method in which chamfering is carried out after slicing, then planar grinding of one surface is carried out, then etching to remove residual strain is carried out if necessary, then washing is carried out, and then both surfaces are finished by chemical polishing (Japanese Patent Application Laid-open Nos. H9-260314, H9-270396), and a method in which chamfering is carried out after slicing, then planar grinding of one surface and lapping are carried out, then dry etching is carried out, and then both surfaces are finished by chemical polishing (Japanese Patent Application Laid-open No. 9-260314), have been proposed.
Various problems have come to the fore with lapping devices used in conventional manufacturing processes. For example, as the diameter of wafers increases, the lapping device must be made larger, and the costs of consumable materials and the device increase; as the diameter of wafers increases and the lapping devices become larger, the load on workers increases; as the amount of consumable materials required increases, the amount of industrial waste (waste polishing dust) increases. Moreover, if one-surface grinding is carried out immediately after slicing, then the undulations caused by the wire saw cannot be removed.
A means by which the above-mentioned problems relating to the lapping device can be resolved is to follow one of the various proposals described above in which a double-headed grinding machine is used in place of the lapping device.
However, if a wafer is manufactured using a double-headed grinding machine, then minute surface undulations (height of a few tens of nm, period of a few mm) appear on the surfaces of the wafer due to the double-headed grinding step.
An object of the present invention is to provide a method of manufacturing a semiconductor wafer in which manufacturing efficiency is improved by grinding using a double-headed grinding machine, and minute surface undulations arising through the grinding are reduced, allowing more uniform surfaces to be obtained.
The present inventors conducted various studies for the purpose of adopting a double-headed grinding step and also combining this step with a step for removing minute surface undulations arising through the double-headed grinding. As a result, the present inventors arrived at the present invention upon discovering that, by processing a wafer after slicing using a double-headed grinding machine, a strained layer and a macroscopic undulation component formed on the wafer surfaces during slicing are removed, and the degree of flatness of the wafer is improved, and that by subsequently carrying out both-surfaces lapping, minute surface undulations that arise during the double-headed grinding are removed.
The present invention thus provides a method of manufacturing a semiconductor wafer comprising a double-headed grinding step, a both-surfaces lapping step, and a both-surfaces polishing step in that order.
Moreover, the present inventors also propose methods of manufacturing a semiconductor wafer in which, in the above-mentioned method, a periphery chamfering step is used after the double-headed grinding step, the both-surfaces lapping step is carried out using elastic platen, and/or a chemical etching step or a grinding step using a single side grinding machine of inversion type optionally followed by an alkali etching step is used after the both-surfaces lapping step.
According to the present invention, when obtaining a semiconductor wafer from a monocrystalline ingot, by carrying out lapping after double-headed grinding, a high-precision semiconductor wafer having no minute undulations (height of 10 to 100 nm, period of 1 to 10 mm) can be manufactured with the amount of waste polishing slurry discharged in the lapping step being reduced to about one quarter.
The present invention relates to obtaining, from a monocrystalline ingot, a semiconductor wafer having a high degree of flatness and little processing-induced strain; by carrying out lapping after double-headed grinding, a high-precision semiconductor wafer having both surfaces polished and having no minute surface undulations can be obtained, the amounts of consumable materials used can be reduced, and manufacturing can be carried out efficiently.